Cash married fellow singer June Carter in 1968 and his second marriage is the focus of the Hollywood film starring Joaquin Phoenix and Reese Witherspoon.

In November, Kathy Cash said: "My mom was basically a nonentity in the entire film except for the mad little psycho who hated his career.

"She loved his career and was proud of him until he started taking drugs and stopped coming home."

Director James Mangold responded: "We interviewed Kathy as well as her mother Vivian in the making of the movie, but it's very hard for kids growing up in a family seeing stuff like this dramatised in front of them."